Anatomy

Neurovascular structures

The course of the axillary nerve must be kept in mind.

Note: The anterior motor branch of the axillary nerve crosses the humerus horizontally about 6 cm distal to the lateral border of the acromion. This distance does not significantly vary and is reliable.

Axillary nerveBefore incising the skin, mark the distal limit of the approach, 5cm below the acromion, which is 1 cm above the course of the axillary nerve.
If a plate is to be passed underneath the axillary nerve, as in minimally invasive plate osteosynthesis (MIPO), mark a second line 2 cm distal to the first, below which the axillary nerve should not be encountered. The space between these two lines is the danger zone on the lateral humerus.

Exposure of the middle third part of the deltoid muscle

Expose the middle third (acromial) part of the deltoid muscle and split the muscle between its fibers.

For maximum exposure, split the deltoid up to the margin of the acromion, but do not split it distally more than 5 cm from its origin to avoid damaging the axillary nerve and paralyzing the anterior part of the deltoid.

Palpate the axillary nerve on the deep surface of the deltoid muscle, distal to the incision. This nerve encircles the proximal humerus a little less than half way from the lateral margin of the acromion to the insertion of the deltoid muscle.

Hemorrhagic subdeltoid bursal tissue may need to be excised to expose the humeral head.

Pearl: stay suture
In order to protect the axillary nerve from uncontrolled distal dissection, a stay suture may be placed at the inferior border of the deltoid split.